Colorado’s laws on labeling and child-resistant packaging have been unable to stop an increase of young kids ending up in the emergency room after accidentally consuming marijuana, according to a new study published online Monday in the medical journal JAMA Pediatrics.

Vince Chandler, The Denver Post

Popular marijuana-infused edibles are display at Denver marijuana dispensary The Health Center.

The study — led by a doctor at the University of Colorado Anschutz Medical Campus — found that emergency room visits and poison-control calls for kids 9 and younger who consumed pot in Colorado jumped after recreational marijuana stores opened. About twice as many kids visited the Children’s Hospital Colorado emergency room per year in 2014 and 2015 as did in years prior to the opening of recreational marijuana stores, according to the study. Annual poison-control cases increased five-fold, the study found.

“We were expecting an increase,” said Dr. Sam Wang, the study’s lead author. “As far as the poison center, we were a little surprised at the amount of the increase.”

The overall numbers, though, are still relatively low and account for a small fraction of all accidental exposures.

Sixteen kids age 9 and younger went to the Children’s ER for marijuana in 2015, and, even with the post-legalization jump, marijuana exposure cases account for about six out of every 1,000 emergency room visits for ingestions, according to the study. Marijuana-related poison-control calls for kids 9 and younger make up about two out of every 1,000 calls, the study reports.

“Pharmaceuticals and household products still account for most toddler exposures because they are much more common and available in the household,” the study’s authors wrote. “However, as marijuana becomes more available, exposures may continue to increase.”

Particularly troubling to the researchers is that these kinds of accidental exposures to marijuana were exactly what lawmakers and regulators hoped to prevent when adopting rules on packaging and labeling. Colorado requires that marijuana be sold in resealable child-proof containers. Rules soon to go into effect will mandate that edible marijuana products be stamped with a special symbol, and a law passed this year will eventually ban marijuana edibles in the shapes of animals or fruit.

Wang said he expects the symbol will do little to curb accidental ingestions by young kids — the median age of patients at both the Children’s ER and in poison-control cases was about 2 years old, well before reading age — but he said the ban on certain shapes that are appealing to kids could help.

“I think we need more evidence to figure out what is the most helpful way to do this,” he said.

The study’s authors found that edibles accounted for almost half of all accidental ingestion cases seen at Children’s Hospital, with a parent being the most likely source of the marijuana. Almost half of the exposures in 2014 and 2015 involved cannabis purchased at a recreational marijuana shop, according to the study.

“Ingestion of edible products continues to be a major source of marijuana exposures in children and poses a unique problem because no other drug is infused into a palatable and appetizing form,” the authors wrote.

Most of the time, the problems caused by these ingestions are minor, according to the study. At Children’s, the median length of visit is 11 hours, though about a third of kids are admitted into inpatient care or even the intensive-care unit. One 3-year-old at the hospital had to be intubated because of breathing problems brought on by the ingestion, and an 8-month-old, “received continuous positive pressure for respiratory insufficiency.”

In calls to poison control, nearly three-quarters of kids had no or minor effects, but four children suffered major effects, according to the study. There was also a reported death, of an 11-month old who initially arrived at a hospital unresponsive and with a rapid heart beat. A urine drug screen came back positive for THC, though the study notes that the connection between the death and marijuana is unclear.